The present invention relates to a prismatic rechargeable battery module in which electrode plates and electrolyte are contained and sealed in a prismatic battery case, and electrode terminals are provided protruding from both ends of this prismatic battery case in the longitudinal direction. More particularly, the present invention relates to an improved structure for the electrode terminals of such rechargeable battery module.
Because of their excellent energy density, nickel metal hydride batteries and other such alkaline rechargeable batteries have in recent years come to be utilized as the power source for electric automobiles, for example. In an effort to obtain a large output while preserving a compact size, a sealed prismatic rechargeable battery has been proposed in Japanese Laid-Open Patent Application H7-161377, for instance, in which a prismatic battery case holds an electrode plate group in which positive electrode plates and negative electrode plates are stacked parallel to the long-side plane of the case with separators imposed therebetween, and the case is sealed.
As shown in FIG. 7, with this type of sealed prismatic rechargeable battery, positive and negative electrode terminals 44 and 45 connected via leads to numerous positive electrode plates and negative electrode plates of an electrode plate group are provided protruding from the top of a lid 43 that seals the top opening of a battery case 42. Numeral 46 is a safety vent that releases internal gas when the pressure rises above a certain point within the battery case 42.
When used as a battery power source, these sealed prismatic batteries (battery modules) 41 are lined up in one or a plurality of rows with their long-side surfaces facing each other and are electrically connected in series by successively connecting the terminals 44 and 45 of the positive and negative electrodes of adjacent battery modules 41, the result of which is that a specific output voltage is obtained. However, a problem with thus electrically connecting numerous battery modules 41 over the lids 43 thereof is that the complicated connecting structure drives up the cost.
In view of this, as shown in FIG. 8, there is proposed a structure in which a plurality of cells are housed in a flat, prismatic battery case 52 in the longitudinal direction thereof and are serially connected inside the battery case 52 to configure a battery module 51, and electrode terminals 54 are provided protruding from the end walls 53 in the longitudinal direction thereof.
With a battery module 51 structured such as his, far fewer connections of the electrode terminals 54 outside of the battery module 51 are required to obtain given output voltage, the cost is lower, and a compact battery power source can be obtained.
Still, with the structure of the battery module 51 shown in FIG. 8, in the event of a collision of the electric vehicle in which this battery module is installed, for instance, there is the danger that the struck object will hit the battery module 51 from the side and that the impact will be borne directly by the electrode terminals 54. The problem if this should happen is that the electrode terminals 54 may move so far that a short-circuit occurs.
Another problem is that, the battery case 52 of this battery module 51 is manufactured by injection molding with a one-point gate 55 located in the middle of the bottom surface as shown in FIG. 9A, or with a two-point gate 56 provided symmetrically on either side of the center line in the longitudinal direction as shown in FIG. 9B. In this case, as shown in FIG. 10, the resin splits up and flows to the right and left sides at the each of the terminal holes 57 provided for the mounting of the electrode terminals 54 in the end walls of the battery case 52, after which these flows come into contact along the center line above each terminal hole 57, and consequently a weld line 58 is created along the center line above the terminal holes 57.
In addition to the fact that the flows of resin do not merge completely at this weld line 58, resulting in a portion of lower strength, the portions located long the center lines above the terminal holes 57 have the smallest cross sectional area, and stress builds up these portions. Therefore, if the internal pressure of the battery case 52 should rise, or if the electrode terminals 54 should be subjected to an external force or vibration, cracks will tend to develop at the weld lines 58, which is a problem in that adequate attachment strength cannot be ensured for the electrode terminals 54.
A further problem is that, these battery modules 51 are lined up so that their long-side surfaces face each other and bound together with end plates disposed at the two ends thereof to constitute a battery pack, and in such state, the long-side surfaces of the battery modules 51 are tightly held together, but the end walls are not, so if the internal battery pressure rises there is the danger that the end walls will become distended and have an adverse effect on the connections of the electrode terminals 54.
Furthermore, with is type of battery module 51, when external wiring or a bus bar connecting the battery modules 51 is connected to the electrode terminals 54, these are clamped with a nut, but this results in a large rotational torque acting on the electrode terminals 54 at the time of connection, and a suitable means for stopping the rotation of the electrode terminals 54 is required.
A conventional anti-rotation means generally involves extending the anti-rotation component as far as possible past the electrode terminals 54 and engaging the distal end thereof with part of the battery case 52, but a problem is that because the rotational torque is received by point engagement between the battery case and the distal end of the anti-rotation component, excessive stress acts on the engagement component and tends to break the distal end of the anti-rotation component, but if an attempt is made to reduce the action load, then the anti-rotation component ends up being larger.
The present invention was conceived in light of the above problems encountered in the past, and it is an object thereof to provide a prismatic rechargeable battery module with which the electrode terminals do not readily bear the impact if the battery module is hit by an object from the side, with which a suitable state of electrical connection can be maintained even if an external force acts on the electrode teals or the internal battery pressure rises, with which the rotation of the electrode terminals can be stopped with a compact structure, and which affords high reliability with respect to loads against the electrode terminals.